Some machine guns have automatic firing mechanisms operated by barrel recoil produced by each live bullet as it is fired. Since blank rounds used for training purposes do not have bullets, such machine guns are not capable of firing automatically when blanks are used. This has led to the development of blank firing attachments that use the pressure of gases generated in firing blank rounds to cause barrel recoil.
The known blank firing attachments cannot be easily or reliably adjusted for the correct rate of fire and cannot be adjusted to fire automatically in the temperature extremes encountered, for example, in Canade and Northern Europe. Other problems include difficulties in cleaning and maintenance, and the requirement to replace the service barrel with a barrel dedicated to blank firing.